The invention relates to a process for the preparation of polymerizable alkoxysilyl siloxanes.
In recent years, organic-inorganic hybrid resins have received much attention in the literature due to their unique electrical, optoelectronic and mechanical properties. Much work is currently focused on the synthesis of crosslinked glass-like matrices composed of Sixe2x80x94Oxe2x80x94Si linkages employing sol-gel techniques that involve the acid or base catalyzed hydrolysis of tri- or tetra-alkoxysilanes. The resulting organic-inorganic hybrid resins have many potential applications, including nonstick release coatings, adhesives, abrasion-resisting coatings for plastics, fiber optic coatings, reinforced composites and optical wave guides. However, traditional sol-gel techniques for their synthesis have a number of drawbacks which have limited their use. First, sol-gel chemistry is slow, often requiring days or weeks for the hydrolysis of the alkoxysilane to proceed to completion. Second, during hydrolysis and subsequent condensation of the resulting silanols, a highly porous, crosslinked matrix resin is formed. If the hydrolysis is carried out too rapidly, the fragile matrix can fracture. Third, during the hydrolysis, there is always considerable shrinkage of the resin matrix. Densification of the initially formed porous matrix by calcination is often required to produce specimens with good cohesive and mechanical strength. Finally, the modification of sol-gel matrices through the incorporation of functionalized alkoxysilane precursors is sometimes difficult, due to the difference in the hydrolysis rates of the components or to their phase separation during the cohydrolysis step.
U.S. Pat. No. 6,069,259 describes a process for the production of an oligomeric alkoxysiloxane substituted with functional groups, including epoxy or 1-alkenyl ether. In the process, hydrolysis/condensation of a trialkoxysilane bearing functional groups is catalyzed by an ion exchange resin (IER).
The process yields resins with high reactivity and low volatility that can be prepared with controllable molecular weights. One drawback to the process is the high intrinsic cost of the starting materials. Accordingly, there is a need for a streamlined, lower cost process for the production of functionalized siloxane monomers and oligomers.
A new generally applicable synthetic approach that can be employed to prepare a family of silicone-epoxy resins using simple, readily available precursors has been unexpectedly discovered. These resins undergo facile cationic photopolymerization to yield organic-inorganic hybrid resins with a wide range of properties.
Accordingly, in one aspect, the present invention relates to a process for the preparation of an alkoxysilyl silane or siloxane containing at least one polymerizable functional group selected from epoxy, vinyl ether, 1-propenyl ether, acrylate and methacrylate. The process comprises selectively reacting at least one compound of formula I 
with at least one compound chosen from A or B, to form a monohydrosilane or monohydrosiloxane; and reacting the monohydro compound with at least one compound chosen from A and B, to form an alkoxysilyl silane or siloxane, with the proviso that when A is used in step (a), B is used in step (b), and when B is used in step (a), A is used in step (b). A is defined as a compound containing at least one vinyl or allyl group and at least one group selected from epoxy, vinyl ether, 1-propenyl ether, acrylate and methacrylate; B is a compound containing at least one vinyl or allyl group and at least one dialkoxysilyl or trialkoxysilyl group; and R1-R4 are independently hydrogen, alkyl, haloalkyl, arylalkyl, aryl or heterocyclic; and n is 0 or an integer from 1 to 100.
In another aspect, the invention relates to a process for the preparation of an alkoxysilyl silane or siloxane substituted with a polymerizable epoxy, vinyl ether, 1-propenyl ether, acrylate or methacrylate group. The process comprises forming an alkoxysilyl silane or siloxane, as described above; and, in the presence of an ion exchange resin, reacting 0.5 to 2.5 equivalents water with the alkoxysilyl compound; and separating the ion exchange resin from a product of the reaction.
In the context of the present invention, alkyl is intended to include linear, branched, or cyclic hydrocarbon structures and combinations thereof. Lower alkyl refers to alkyl groups of from 1 to 4 carbon atoms. Lower alkyl groups include methyl, ethyl, n-propyl, isopropyl, and n-, s- and t-butyl. Preferred alkyl groups are those of C20 or below. Cycloalkyl is a subset of alkyl and includes cyclic hydrocarbon groups of from 3 to 8 carbon atoms. Examples of cycloalkyl groups include cyclopropyl, cyclobutyl, cyclopentyl, and norbornyl
Alkoxy or alkoxyl refers to groups of from 1 to 8 carbon atoms of a straight, branched, cyclic configuration and combinations thereof attached to the parent structure through an oxygen. Examples include methoxy, ethoxy, propoxy, isopropoxy, cyclopropyloxy, and cyclohexyloxy. Lower alkoxy refers to groups containing one to four carbons.
Acyl refers to groups of from 1 to 8 carbon atoms of a straight, branched, cyclic configuration, saturated, unsaturated and aromatic and combinations thereof, attached to the parent structure through a carbonyl functionality. One or more carbons in the acyl residue may be replaced by nitrogen, oxygen or sulfur as long as the point of attachment to the parent remains at the carbonyl. Examples include acetyl, benzoyl, propionyl, isobutyryl, t-butoxycarbonyl, and benzyloxycarbonyl. Lower-acyl refers to groups containing one to four carbons.
Aryl and heteroaryl mean a 5- or 6-membered aromatic or heteroaromatic ring containing 0-3 heteroatoms selected from nitrogen, oxygen or sulfur; a bicyclic 9- or 10-membered aromatic or heteroaromatic ring system containing 0-3 heteroatoms selected from nitrogen, oxygen or sulfur; or a tricyclic 13- or 14-membered aromatic or heteroaromatic ring system containing 0-3 heteroatoms selected from, oxygen or sulfur. Each of these rings is optionally substituted with 1-3 lower alkyl, substituted alkyl, substituted alkynyl, carbonyl, nitro, halo, haloalkyl, hydroxy, alkoxy, OCH(COOH)2, cyano, primary amino, secondary amino, acylamino, phenyl, benzyl, phenoxy, benzyloxy, heteroaryl, or heteroaryloxy; each of said phenyl, benzyl, phenoxy, benzyloxy, heteroaryl, and heteroaryloxy is optionally substituted with 1-3 substitutents selected from lower alkyl, alkenyl, alkynyl, halogen, hydroxy, haloalkyl, alkoxy, cyano, phenyl, benzyl, benzyloxy, carboxamido, heteroaryl, heteroaryloxy, nitro or xe2x80x94NRR (wherein R is independently H, lower alkyl or cycloalkyl, and xe2x80x94RR may be fused to form a cyclic ring with nitrogen). The aromatic 6- to 14-membered carbocyclic rings include, for example, benzene, naphthalene, indane, tetralin, and fluorene; and the 5- to 10-membered aromatic heterocyclic rings include, e.g., imidazole, pyridine, indole, thiophene, benzopyranone, thiazole, furan, benzimidazole, quinoline, isoquinoline, quinoxaline, pyrimidine, pyrazine, tetrazole and pyrazole.
Alkylaryl means an alkyl residue attached to an aryl ring. Examples are benzyl and phenethyl. Heteroarylalkyl means an alkyl residue attached to a heteroaryl ring. Examples include pyridinylmethyl and pyrimidinylethyl.
Heterocycle means a cycloalkyl or aryl residue in which one to two of the carbons is replaced by a heteroatom such as oxygen, nitrogen or sulfur. Examples of heterocycles that fall within the scope of the invention include pyrrolidine, pyrazole, pyrrole, indole, quinoline, isoquinoline, tetrahydroisoquinoline, benzofuran, benzodioxan, benzodioxole (commonly referred to as methylenedioxyphenyl, when occurring as a substituent), tetrazole, morpholine, thiazole, pyridine, pyridazine, pyrimidine, thiophene, furan, oxazole, oxazoline, isoxazole, dioxane, and tetrahydrofuran.
Substituted alkyl, aryl, cycloalkyl, or heterocyclyl refer to alkyl, aryl, cycloalkyl, or heterocyclyl wherein up to three H atoms in each residue are replaced with halogen, haloalkyl, hydroxy, lower alkoxy, carboxy, carboalkoxy, carboxamido, cyano, carbonyl, nitro, primary amino, secondary amino, alkylthio, sulfoxide, sulfone, acylamino, amidino, phenyl, benzyl, heteroaryl, phenoxy, benzyloxy, heteroaryloxy, or substituted phenyl, benzyl, heteroaryl, phenoxy, benzyloxy, or heteroaryloxy.